One thing that people seems missing: GTX 1080 (and 1070 IIRC) Has DisplayPort 1.4. The chip and the cards weren't certified by VESA for DP 1.3/1.4 (the 1.4 has not transmission changes, just few more compression support).
Once those cards will be certified, the only thing that you'll need is a firmware support, the cable remains the same with the same 20 pin connectors, so you'll be able to use GTX 1070/1080p on DisplayPort 1.3/1.4 monitors.
Ref: https://www.nvidia.com/en-us/geforce/products/10series/geforce-gtx-1080/
